1. Field of the Invention
The present invention relates to an image analysis device, an image analysis method, and a non-transitory computer-readable recording medium that stores an image analysis program that analyze a radiographic image acquired by imaging a photographic subject.
2. Description of the Related Art
In the related art, when capturing a radiographic image of a photographic subject by using radiation rays that pass through the photographic subject, especially, if the thickness of the photographic subject is large, the radiation rays are scattered inside the photographic subject, and the contrast of the acquired radiographic image may deteriorate due to the scattered radiation rays (hereinafter, referred to as scattered rays). Thus, when capturing the radiographic image, a scattered ray removal grid (hereinafter, referred to as a grid) is disposed between the photographic subject and a radiation detector that detects radiation rays to obtain a radiographic image so that the radiation detector is not irradiated with scattered rays before imaging, in some cases. If the imaging is performed using the grid, the radiation detector is not easily irradiated with the radiation rays scattered by the photographic subject, and thus, it is possible to enhance the contrast of the radiographic image.
On the other hand, if the imaging is performed using the grid, a photographic subject image and a stripe pattern (grid stripe) corresponding to the grid are included in the radiographic image, which deteriorates the image quality of the image. Accordingly, a process of removing a grid stripe from a radiographic image captured using a grid is known (see JP2003-260053A, JP2000-083951A, JP2003-008885A, and JP1994-014911A (JP-H06-014911A)). Further, the grid stripe is generated when a stationary grid for performing stationary imaging is used, and is not generated in the radiographic image when a rocking grid (Bucky-Potter grid) for rocking imaging is used. Thus, when the rocking grid is used, it is possible to obtain a radiographic image with high image quality without a grid stripe, without performing the above-mentioned grid stripe suppression process.
In this regard, since a lead material or the like that does not transmit radiation rays, and an inter-space material made of aluminum, fiber or the like that transmits radiation rays are alternately disposed in a fine grating density of about 4.0 lines/mm, for example, the grid has a large weight. In portable imaging performed in a hospital room or the like, it is necessary to dispose a grid between a patient who is on a bed and a radiation detector. Accordingly, the weight of the grid causes an increased workload of a grid mounting operation to a photographer, and increased burdens of the patient in imaging. Further, in the case of a convergence type grid, there is a concern that density unevenness occurs in a radiographic image due to oblique incidence of radiation rays.
Thus, a process of performing capturing of a radiographic image without using a grid and assigning an image quality improvement effect acquired by removing scattered rays by the grid to the radiographic image using image processing has been proposed (see JP1990-244881A (JP-H02-244881A)). According to the technique disclosed in JP1990-244881A (JP-H02-244881A), a photographic subject image is classified for each pixel of the photographic subject image according to a body thickness depending on an image signal, a total scattered ray distribution generated by a photographic subject having each classified body thickness is calculated, and the total scattered ray distribution is subtracted from the radiographic image to obtain a radiographic image in which a component of scattered rays is removed. According to the technique disclosed in JP1990-244881A (JP-H02-244881A), since the grid is not necessary in imaging, it is possible to reduce the burden of the patient in imaging, and to prevent deterioration of image quality due to density unevenness and a grid stripe.
However, in a radiography system capable of acquiring three types of radiographic images of a radiographic image captured using a stationary grid, a radiographic image captured using a Bucky-Potter grid, and a radiographic image captured without using a grid, when a process of removing a grid stripe with respect to all of the acquired radiographic images is performed, a grid stripe suppression process is performed even with respect to the radiographic image captured without using the grid. Contrarily, when a scattered ray suppression process is performed, the scattered ray suppression process is performed even with respect to the radiographic image captured using the grid. In this way, if an unnecessary process in a specific radiographic image is performed with respect to the radiographic image, the image quality of the radiographic image greatly deteriorates, and thus, it is difficult to perform diagnosis with high efficiency.
Thus, according to JP2003-260053A and JP2000-083951A, for example, a grid is retained in a frame-shaped retention section in which a protrusion portion is disposed at a different position according to a grid type, and a micro-switch is provided at a position on a device that faces a protrusion portion of the grid, and the micro-switch is turned on according to the grid type. JP2003-260053A and JP2000-083951A disclose a technique for determining the presence or absence of the grid, or the type thereof, and performing image processing depending on the presence or absence of the grid, or the type thereof, using the above configuration. Further, JP2003-260053A and JP2000-083951A disclose a technique for detecting values of parameters that are changed due to a load applied to a motor that rocks a grid to determine the presence or absence of the grid, or the weight thereof.